BRUSSELS, Belgium- The world faces increased hunger and water shortages in the poorest countries, massive floods and avalanches in Asia, and species extinction unless nations adapt to climate change and halt its progress, according to a report approved Friday by an international conference on global warming.

Agreement came after an all-night session during which key sections were deleted from the draft and scientists angrily confronted government negotiators who they feared were watering down their findings.

“It has been a complex exercise,” said Rajendra Pachauri, chairman of the Intergovernmental Panel on Climate Change.

Several scientists objected to the editing of the final draft by government negotiators but, in the end, agreed to compromises. However, some scientists vowed never to take part in the process again.

Five days of negotiations reached a climax when the delegates removed parts of a key chart highlighting devastating effects of climate change that kick in with every rise of 1.8 degrees, and in a tussle over the level of scientific reliability attached to key statements.

There was little doubt about the science, which was based on 29,000 sets of data, much of it collected in the last five years. “For the first time we are not just arm-waving with models,” Martin Perry, who conducted the grueling negotiations, told reporters.

The United States, China and Saudi Arabia raised many of the objections to the phrasing, often seeking to tone down the certainty of some of the more dire projections.

The final IPCC report is the clearest and most comprehensive scientific statement to date on the impact of global warming mainly caused by man-induced carbon dioxide pollution.

“The poorest of the poor in the world _ and this includes poor people in prosperous societies _ are going to be the worst hit,” Pachauri said. “People who are poor are least able to adapt to climate change.”

The report said up to 30 percent of species face an increased risk of vanishing if global temperatures rise 3.6 degrees above the average in the 1980s and 1990s.

Areas in drought will become even more dry, adding to the risks of hunger and disease, it said. The world will face heightened threats of flooding, severe storms and the erosion of coastlines.

“This is a glimpse into an apocalyptic future,” the Greenpeace environmental group said of the final report.

Without action to curb carbon emissions, man’s livable habitat will shrink starkly, said Stephen Schneider, a Stanford scientist who was one of the authors. “Don’t be poor in a hot country, don’t live in hurricane alley, watch out about being on the coasts or in the Arctic, and it’s a bad idea to be on high mountains with glaciers melting.”

“We can fix this,” by investing a small part of the world’s economic growth rate, said Schneider. “It’s trillions of dollars, but it’s a very trivial thing.”

Negotiators pored over the 21-page draft meant to be a policy guide for governments. The summary pares down the full 1,572-page scientific assessment of the evidence of climate change so far, and the impact it will have on the Earth’s most vulnerable people and ecosystems.

More than 120 nations attended the meeting. Each word was approved by consensus, and any change had to be approved by the scientists who drew up that section of the report.

Parry denied the hard-fought editing process resulted in a watered-down version, but acknowledged that “certain messages were lost.”

At one point early Friday, it looked like the report “was not going to be accepted. It was very, very close to that point,” said David Karoly, one of the scientific authors from the University of Oklahoma.

Though weakened by the deletion of some elements, the final report “will send a very, very clear signal” to governments, said Yvo de Boer, the U.N.’s top climate official.

The summary will be presented to the G8 summit of the world’s richest nations in June, when the European Union is expected to renew appeals to President Bush to join in international efforts to control emissions of fossil fuels.

This year’s series of reports by the IPCC were the first in six years from the prestigious body of 2,500 scientists, formed in 1988. Public awareness of climate change gave the IPCC’s work unaccustomed importance and fueled the intensity of the closed-door negotiations during the five-day meeting.

“The urgency of this report prepared by the world’s top scientists should be matched by an equally urgent response from governments,” said Hans Verolme, director of the global climate change program of the World Wide Fund for Nature.

At the final session, the conference snagged over a sentence that said the impact of climate change already were being observed on every continent and in most oceans.

“There is very high confidence that many natural systems are being affected by regional climate changes, particularly temperature increases,” said the statement on the first page of text.

But China insisted on striking the word “very,” injecting doubt into what the scientists argued were indisputable observations. The report’s three authors refused to go along with the change, resulting in an hours-long deadlock that was broken by a U.S. compromise to delete any reference to confidence levels.

It is the second of four reports from the IPCC this year; the first report in February laid out the scientific case for how global warming is happening. This second report is the “so what” report, explaining what the effects of global warming will be.

For the first time, the scientists broke down their predictions into regions, and forecast that climate change will affect billions of people.

North America will experience more severe storms with human and economic loss, and cultural and social disruptions. It can expect more hurricanes, floods, droughts, heat waves and wildfires, it said. Coasts will be swamped by rising sea levels. In the short term, crop yields may increase by 5 percent to 20 percent from a longer growing season, but will plummet if temperatures rise by 7.2 degrees.

Africa will be hardest hit. By 2020, up to 250 million people are likely to be exposed to water shortages. In some countries, food production could fall by half, it said.

Parts of Asia are threatened with massive flooding and avalanches from melting Himalayan glaciers. Europe also will see its Alpine glaciers disappear. Australia’s Great Barrier Reef will lose much of its coral to bleaching from even moderate increases in sea temperatures, the report said.

Separately, an independent organization that keeps tabs on glacial melting in Austria’s Alps said its latest survey confirms that the ice sheets continue to shrink significantly and predicted most will vanish by the end of the century.

The Austrian Alpine Association said experts measured 105 of Austria’s 925 glaciers last year and found they had receded by an average of 52 1/2 feet, with one of the sheets shrinking a dramatic 262 feet during 2006.